WASHINGTON (CNN) - Former Wisconsin Gov. Tommy Thompson has decided to officially enter the race for the GOP presidential nomination, and has tentatively picked Wednesday, April 4, to make an official announcement, according to a campaign aide.

Details for the announcement, including the location, have not been finalized.

The former Health and Human Services Secretary set up a presidential exploratory committee in December and a filed a statement of candidacy with the Federal Election Commission in January.

Thompson will be a guest Tuesday on "The Situation Room with Wolf Blitzer" at 4 p.m. ET.